Negative Nonadditivity Research Articles

Disordered hyperuniformity in two-component nonadditive hard-disk plasmas

We study the behavior of a classical two-component ionic plasma made up of nonadditive hard disks with additional logarithmic Coulomb interactions between them. Due to the Coulomb repulsion, long-wavelength total density fluctuations are suppressed and the system is globally hyperuniform. Short-range volume effects lead to phase separation or to heterocoordination for positive or negative nonadditivities, respectively. These effects compete with the hidden long-range order imposed by hyperuniformity. As a result, the critical behavior of the mixture is modified, with long-wavelength concentration fluctuations partially damped when the system is charged. It is also shown that the decrease of configurational entropy due to hyperuniformity originates from contributions beyond the two-particle level. Finally, despite global hyperuniformity, we show that in our system the spatial configuration associated with each component separately is not hyperuniform, i.e., the system is not "multihyperuniform."

The effects of geometric non-additivity on the wetting of symmetric mixtures at a wall

The paper discusses the behavior of symmetric binary mixtures of Lennard-Jones particles in contact with non-selective smooth walls. Using the Monte Carlo simulation method in the grand canonical ensemble, we have elucidated the effects of negative and positive geometric non-additivity on the wetting behavior in a series of systems characterized by different strength of the fluid-wall interaction.It has been shown that even in the case of mixtures which do not exhibit demixing transition the geometric non-additivity considerably changes the wetting behavior of symmetric mixtures. In particular, it has been demonstrated that the structure and stability of the bulk solid and liquid phases play an important role, and lead to non-monotonous changes of the wetting temperature when the geometric non-additivity changes. It has been also shown that the systems with negative geometric non-additivity exhibit a triple-point wetting over a certain range of the surface potential strength. In such cases, the first-order wetting transition occurs when the wetting temperature is higher than the bulk triple point temperature and becomes a continuous transition (critical wetting) when the triple wetting occurs. On the other hand, the systems with positive geometric non-additivity have not been observed to show the triple point wetting, and the wetting temperature decreases smoothly when the strength of the surface field increases. For sufficiently strong surface fields, the adsorbed film develops in a layer-by-layer mode, independently of the geometric non-additivity.

Effects of geometrical and energetic nonadditivity on the phase behavior of two-component symmetric mixtures.

Using Monte Carlo simulation methods in the grand-canonical ensemble, we have studied the phase behavior of three-dimensional symmetric binary mixtures of Lennard-Jones particles. We have also elucidated the effects of geometric and energetic nonadditivity on the phase behavior. Phase diagrams for several systems have been evaluated. We have demonstrated that in completely miscible mixtures the geometrical nonadditivity (negative as well as positive) stabilizes a liquid phase leading to a gradual increase of the critical temperature. The mechanism leading to such behavior is different when the system shows negative and positive geometrical nonadditivity. In the case of systems with negative energetic nonadditivity, which may exhibit demixing transition in the liquid phase, their phase behavior is also strongly affected by the geometric non-additivity. The systems with negative geometric nonadditivity have been demonstrated to show reentrant miscibility, while those with positive geometric nonadditivity show enhanced tendency toward mixing at sufficiently high temperatures. We have evaluated phase diagrams for several systems.

Reentrant miscibility in two-dimensional symmetrical mixtures

The Monte Carlo simulation method in the grand canonical ensemble is used to study the phase behavior of two-dimensional symmetrical binary mixtures of Lennard-Jones particles with negative nonadditivity and the weaker interaction between the pairs of unlike than between the pairs of like particles. We have determined the evolution of the phase diagram topology when the parameters describing the interaction between unlike particles vary. It has been found that such systems may exhibit reentrant miscibility in the liquid and the solid phases.

Monte Carlo simulation of the nonadditive restricted primitive model of ionic fluids: Phase diagram and clustering

We report an accurate Monte Carlo calculation of the phase diagram and clustering properties of the restricted primitive model with nonadditive hard-sphere diameters. At high density the positively nonadditive fluid shows more clustering than in the additive model and the negatively nonadditive fluid shows less clustering than in the additive model; at low density the reverse scenario appears. A negative nonadditivity tends to favor the formation of neutrally charged clusters starting from the dipole. A positive nonadditivity favors the pairing of like ions at high density. The critical point of the gas-liquid phase transition moves at higher temperatures and higher densities for a negative nonadditivity and at lower temperatures and lower densities for a positive nonadditivity. The law of corresponding states does not seem to hold strictly. Our results can be used to interpret recent experimental works on room temperature ionic liquids.

The restricted primitive model of ionic fluids with nonadditive diameters

The restricted primitive model with nonadditive hard-sphere diameters is shown to have interesting and peculiar clustering properties. We report accurate calculations of the cluster concentrations. Implementing efficient and ad hoc Monte Carlo algorithms we determine the effect of nonadditivity on both the clustering and the gas-liquid binodal. For negative nonadditivity, tending to the extreme case of completely overlapping unlike ions, the prevailing clusters are made of an even number of particles having zero total charge. For positive nonadditivity, the frustrated tendency to segregation of like particles and the reduced space available to the ions favors percolating clusters at high densities.

Life History Shapes Trait Heredity by Accumulation of Loss-of-Function Alleles in Yeast

A fundamental question in biology is whether variation in organisms primarily emerges as a function of adaptation or as a function of neutral genetic drift. Trait variation in the model organism baker's yeast follows population bottlenecks rather than environmental boundaries suggesting that it primarily results from genetic drift. Based on the yeast life history, we hypothesized that population-specific loss-of-function mutations emerging in genes recently released from selection is the predominant cause of trait variation within the species. As retention of one functional copy of a gene in diploid yeasts is typically sufficient to maintain completely unperturbed performance, we also conjectured that a crossing of natural yeasts from populations with different loss-of-function mutations would provide a further efficient test bed for this hypothesis. Charting the first species-wide map of trait inheritance in a eukaryotic organism, we found trait heredity to be strongly biased toward diploid hybrid performance exactly mimicking the performance of the best of the parents, as expected given a complete dominance of functional over nonfunctional alleles. Best parent heterosis, partial dominance, and negative nonadditivity were all rare phenomena. Nonadditive inheritance was observed primarily in crosses involving at least one very poor performing parent, most frequently of the West African population, and when molecularly dissected, loss-of-function alleles were identified as the underlying cause. These findings provide support for that population-specific loss-of-function mutations do have a strong impact on genotype-phenotype maps and underscores the role of neutral genetic drift as a driver for trait variation within species.

The structure, properties, and nature of C–Br⋯F halogen bond involving HArF: Substitution, hybridization, and nonadditivity

Quantum chemical calculations have been performed to investigate the halogen bond of HArF with some brominated hydrocarbons at the MP2/aug-cc-pVTZ level. The C–Br bond in F3CBr–FArH complex is contracted, while it is elongated in other halogen-bonded complexes. However, the C–Br stretch vibration has a small red shift in all complexes. The strength of halogen bond becomes stronger in order of Csp3–Br<Csp2–Br<Csp–Br. The substitution position in CH2CHBr has a prominent effect on the strength of halogen bond. With the number of F atom in CH2CHBr, the halogen bond is stronger and a negative nonadditivity is present for F substitution. The average contribution of each F atom to the interaction energy of halogen bond is estimated to be −4kJ/mol. Additionally, two hydrogen-bonded complexes of BrCCH–FArH and HCCBr-pi-HArF have also been studied. These complexes have been analyzed with the electrostatic potentials and NBO theory.

Radial distribution functions of non-additive hard sphere mixtures via Percus’ test particleroute

Using fundamental density functional theory we calculate the partial radial distribution functions,gij(r), of a binary non-additive hard sphere mixture using either Percus’ test particle approachor inversion of the analytic structure factor obtained via the Ornstein–Zernike route. Wefind good agreement between the theoretical results and Monte Carlo simulation data forboth positive and moderate negative non-additivities. We investigate the asymptotic,, decay of the gij(r) and show that this agrees with the analytic analysis of the contributions to the partialstructure factors in the plane of complex wavevectors. We find the test particle densityprofiles to be free of unphysical artefacts, contrary to earlier reports.

Partially covalent nature and substitution non-additivity of Au-bonding in H2O–AuCH3 complex

Quantum chemical calculations have been performed to study the interaction in H2O–AuCH3 complex. The results show that there is an Au-bonding interaction in the complex. The F substitution in the Au donor molecule enhances this interaction and the methyl group in the Au acceptor molecule also makes it enhance. The F atoms in the Au donor show a positive non-additivity, whereas the methyl groups in the Au acceptor exhibit a negative non-additivity. The Au-bonding is similar to H-bonding, but charge transfer has a greater contribution in this interaction and it exhibits partially covalent nature.

Ab Initio Study of Nonadditivity Effects: Spin−Spin Coupling Constants for Tetrafluoroethene in Ternary π Complexes

C(2)F(4) coupling constants have been evaluated at EOM-CCSD/(qzp,qz2p) in binary complexes with electron donors X (X = HLi, Cl(-), CN(-)) and with the electron acceptor FH, and in ternary complexes FH:C(2)F(4):X in which X and FH are located on opposite faces of the C(2)F(4) pi cloud. The electron donors X and the electron acceptor FH have opposite effects on (1)J(C-C), (1)J(C-F), (2)J(C-F), and (3)J(F-F) in binary complexes. Effects of X and FH on a particular coupling constant in a ternary complex are additive if the change in the coupling constant in this complex relative to C(2)F(4) is within 1 Hz of the sum of the changes in the corresponding binary complexes. This is the case for (1)J(C-F). Both positive and negative nonadditivities are computed for the remaining coupling constants. Although the values of most coupling constants lie between the values for FH:C(2)F(4) and C(2)F(4):X, that is not the case for (2)J(C-F), and the effect of FH is enhanced by the presence of X. Moreover, values of (3)J(F-F) trans and cis for FH:C(2)F(4):X when X is Cl(-) or CN(-) bonded through C are within 1 Hz of the values for the corresponding binary complex C(2)F(4):X. Significant differences can be found between the relative contributions of the PSO, FC, and SD terms to total J and to the nonadditivities of J in ternary complexes FH:C(2)F(4):X.

Comparative study on the nonadditivity of methyl group in lithium bonding and hydrogen bonding

AbstractQuantum chemical calculations at the second‐order Moeller–Plesset (MP2) level with 6‐311++G(d,p) basis set have been performed on the lithium‐bonded and hydrogen‐bonded systems. The interaction energy, binding distance, bond length, and stretch frequency in these systems have been analyzed to study the nonadditivity of methyl group in the lithium bonding and hydrogen bonding. In the complexes involving with NH3, the introduction of one methyl group into NH3 molecule results in an increase of the strength of lithium bonding and hydrogen bonding. The insertion of two methyl groups into NH3 molecule also leads to an increase of the hydrogen bonding strength but a decrease of the lithium bonding strength relative to that of the first methyl group. The addition of three methyl groups into NH3 molecule causes the strongest hydrogen bonding and the weakest lithium bonding. Although the presence of methyl group has a different influence on the lithium bonding and hydrogen bonding, a negative nonadditivity of methyl group is found in both interactions. The effect of methyl group on the lithium bonding and hydrogen bonding has also been investigated with the natural bond orbital and atoms in molecule analyses. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

GaAs thermal oxidation with participation of spatially separated activator oxides (MnO + PbO and MnO + V2O5)

Spatial separation of activator oxides in MnO2 + PbO and MnO2 + V2O5 binary compositions helps to locate the interactions between the oxides that lead to nonlinear joint effects of the compositions on GaAs thermal oxidation. The mutual enhancement of the chemostimulating activity (a positive nonlinear effect) was discovered in the solid phase, whereas vapor-phase processes led to a considerable negative nonadditivity of the joint chemostimulating effect.

Effect of methyl group on the cooperativity of CH···O blue-shifted hydrogen bond in HCHO–HCHO–HCHO cyclic complex

The effect of methyl group on the cooperativity of CH···O blue-shifted hydrogen bond in HCHO–HCHO–HCHO cyclic complex has been studied with quantum chemical calculations at the MP2/6-31+G(d,p) level. We report herein the optimized geometries of the stable structures, their vibrational frequencies, NMR chemical shifts, stabilization energies, and binding energies. The cooperativity of CH···O blue-shifted hydrogen bond varies from −0.57 kcal/mol in triformaldehyde through −0.65 kcal/mol in trimethyltriformaldehyde to −0.79 kcal/mol in trifluorotriformaldehyde. The result indicates that the methyl group has a little enhancing effect on the cooperativity of CH···O blue-shifted hydrogen bond in the cyclic complex. A negative nonadditivity of methyl group is evaluated in enhancing the cooperativity of three CH···O blue-shifted hydrogen bonds. In the formation of the CH···O blue-shifted hydrogen bond, the methyl group in the proton-acceptor plays a positive contribution, whereas that in the proton-donor plays a negative contribution.

Fundamental measure density functional theory for nonadditive hard-core mixtures: The one-dimensional case

We treat a one-dimensional binary mixture of hard-core particles that possess nonadditive diameters. For this model, a density functional theory is constructed following similar principles as an earlier extension of Rosenfeld's fundamental measure theory to three-dimensional nonadditive hard-sphere mixtures. The theory applies to arbitrary positive and moderate negative nonadditivity and reduces to Percus' exact functional in the additive case. Bulk direct correlation functions are obtained as functional derivatives of the excess free energy functional. Results for the partial pair correlation functions in bulk, as calculated via the Ornstein-Zernike route and using the direct correlation functions as input, show very good agreement with results from our Monte Carlo computer simulations of the mixture.

Virial Coefficients and Demixing of Athermal Nonadditive Mixtures

We compute the fourth virial coefficient of a binary nonadditive, hard-sphere mixture over a wide range of deviations from diameter additivity and size ratios. Hinging on this knowledge, we build up a y expansion (Barboy, B.; Gelbart, W. N. J. Chem. Phys. 1979, 71, 3053) in order to trace the fluid-fluid coexistence lines, which we then compare with the available Gibbs-ensemble Monte Carlo data and with the estimates obtained through two refined integral-equation theories of the fluid state. We find that in a regime of moderately negative nonadditivity and largely asymmetric diameters, relevant to the modeling of sterically and electrostatically stabilized colloidal mixtures, the fluid-fluid critical point is unstable with respect to crystallization.

How altruism evolves: assortment and synergy

If one defines altruism strictly at the population level such that carriers of the altruistic genotype are required to experience, on average, a net fitness cost relative to average population members, then altruism can never evolve. This is simply because a genetically encoded trait can only increase in a population (relative to alternative traits) if the mean fitness of individuals carrying this genotype is higher than the population average fitness. This is true whether the genotype of interest encodes a self-serving behaviour such as enhanced predator avoidance, or an altruistic behaviour in which the actor enhances the fitness of those it interacts with more than its own. The paradox in the evolution of altruism is that carriers that are, on average, at a local disadvantage (i.e. compared to those they interact with) can still have higher fitness than the population average and hence can increase overall. The most fundamental explanation for how altruism (defined by local interactions) increases in a population requires that there be assortment in the population such that the benefit from others falls sufficiently often to carriers (and at the same time nonaltruists are stuck interacting more with each other). Nonadditivity if present can play a similar role: when collective cooperation yields synergistic benefits (positive nonadditivity) altruistic behaviour can evolve even in the absence of positive assortment, and when there are diminishing returns for cooperation (negative nonadditivity) the evolution of altruism is hindered (Queller, 1985; Hauert et al., 2006). In their target article Lehmann & Keller (2006) use a form of Hamilton’s rule (1964, 1975) to classify different mechanisms by which helping behaviours can evolve. However, the version they develop tends to obscure the fundamental roles that assortment and nonadditivity play. Their framework also confuses local and population-wide definitions of altruism in making distinctions between nonrelatives and relatives, and what they label as mere ‘cooperation’ vs. true ‘altruism’. We argue that a previous generalization of Hamilton’s rule developed by Queller (1985) makes clear the roles played by assortment and nonadditivity and therefore serves as a better starting point for classifying various proposed models and mechanism of how altruistic traits can evolve.

Demixing can occur in binary hard-sphere mixtures with negative nonadditivity

A binary fluid mixture of nonadditive hard spheres characterized by a size ratio gamma = sigma(2)/sigma(1) < 1 and a nonadditivity parameter Delta = 2 sigma(12)/(sigma(1) + sigma(2)) - 1 is considered in infinitely many dimensions. From the equation of state in the second virial approximation (which is exact in the limit d--> infinity) a demixing transition with a critical consolute point at a packing fraction scaling as eta approximately d2(-d) is found, even for slightly negative nonadditivity, if Delta >-1/8 (ln gamma)(2). Arguments concerning the stability of the demixing with respect to freezing are provided.

Simulation and model development for the equation of state of self assembling non-additive hard chain–hard monomer mixture

Molecular dynamics simulations for a short hard chain composed of a head and three tail groups interacting with non-additive size interactions with a hard sphere solvent were performed. Different densities and non-additivities were used. The equation of state for this mixture was investigated and models based on the first-order thermodynamic perturbation theory (TPT1) and the polymeric analog of the Percus–Yevick approximation (PPY) were developed to predict the compressibility factor of the mixture. The models predicted the compressibilities of the mixtures accurately at zero and negative non-additivities. However, at positive non-additivities, the models overpredicted the compressibilities especially at high densities. The TPT1 model was generally more accurate in predicting the compressibility factor than the PPY model. Microphase separation was observed at high densities and positive non-additivities.

Structure, melting, and order tendencies ofA13B13Lennard-Jones heteroclusters with additive and nonadditive collision diameters

Using constant-energy molecular-dynamics simulations, we studied the lowest-energy structures, melting behavior, and ordering tendencies of ${\mathit{A}}_{13}$${\mathit{B}}_{13}$ Lennard-Jones (LJ) clusters with additive and nonadditive collision diameters. We found that nonadditivity can significantly affect the properties of the LJ clusters. In particular, small negative nonadditivities give rise to nonicosahedral configurations.